Stereoscopic surgical microscopes often possess a system for reflecting in illumination with which an illumination beam path is split by way of a deflection device into an oblique and a zero-degree partial beam, which are switched into the main beam path of the microscope.
Reflected-in beam paths for illumination of a specimen field are used in a wide variety of applications, in particular including ophthalmology. In this context, the patient's eye is usually illuminated directly by the surgical microscope's illumination. If the brightness is excessive, this greatly endangers the retina in particular but also the cornea.
Repeated attempts have therefore been made to exclude or minimize this hazard. For that purpose, for example in U.S. Pat. No. 4,715,704 of Zeiss, an opaque stop whose location is conjugated with the specimen plane was pivoted into the illumination beam path. A stop having a physical and spectral gradient is described in DE-A-101 08 254. These stops all result in a darkening of the specimen field, which of course provides the best eye protection. As a result, however, the surgeon's work is also impeded by a limited view. What is actually desirable is therefore a certain amount of eye protection and sufficient illumination for the surgeon.
One solution consists in an ophthalmological objective of Leica, in which the zero-degree illumination can be swung out by rotating the objective (as of mid-1980).
Olympus proposes shutting off the zero-degree illumination using a shutter (see Japanese Patent publication number 09105866). With both solutions, the harmful zero-degree illumination is shut off, but the specimen field continues to be illuminated by the so-called 6-degree component. The Applicant's Swiss patent application number CH-977/00 makes a proposal in which, by pivoting out various lens elements, the image of the harmful light on the retina is modified in such a way that the harmfulness is considerably reduced.
Olympus proposes shutting off the zero-degree illumination using a shutter (09105866). With both solutions, the harmful zero-degree illumination is shut off, but the specimen field continues to be illuminated by the so-called 6-degree component. The Applicant's Swiss patent application CH-977/00 makes a proposal in which, by pivoting out various lens elements, the image of the harmful light on the retina is modified in such a way that the harmfulness is considerably reduced.
A further device, but one that is complex in terms of optical configuration, is evident from the Carl Zeiss brochure for the OPMI MD®. Here the patient's eye can be illuminated with a built-in oblique illumination system when the red reflection is no longer needed.
Carl Zeiss (in DE-A-402 86 05) and Möller (in DEA-196 50 773) describe an assemblage having two deflection means, in which the first is arranged either partially or entirely shiftably. The further deflection means are arranged close to the observation beam paths, entirely or partially surrounding them. A uniform red reflection is thereby obtained.
In 1998 the Applicant proposed (in WO/A-99/59016) an illumination apparatus in which one oblique light flux and one parallel to the microscope's main axis are created, and can be regulated independently of one another. The disadvantages of this solution are: with a zero-degree prism snorkel, only a portion of the illumination pupil is used; this can result in vignetting and field cutoff. In addition, the zero-degree illumination field is smaller than the 6-degree field. The result of this is that in some circumstances, the red reflection does not occur everywhere in the illuminated field. This arrangement also causes at least three reflections to be imaged on the cornea, which in some circumstances can be undesirable.